1. Field of the Invention
This invention relates to improvements in a method of producing a compound oxide by using a citrating process for compounds of elements, and more particularly to the method of producing the compound oxide by partly citrating the compounds of elements.
2. Description of the Prior Art
Hitherto a variety of methods of producing a compound oxide by using the citrating process for compounds of elements have been carried out in order to prepare raw materials of functional ceramics such as magnetic substances, catalysts, sensors, high temperature superconductors, dielectrics, and photoactive materials. One of such methods is disclosed by C. Marcilly in Journal of American Ceramic Society 53, 56 (1970). In this method, the compound oxide is synthesized under reaction of citrate with nitrate and acetate of metals. Another method is disclosed by Hirabayashi et al in the Bulletin of Japan Metallurgical Society 26, 10 (1987). In this method, citric acid and ethylene glycol are reacted with nitrates of yttrium, barium and copper thereby to synthesize a high temperature superconductive compound oxide.
However, in the above methods, citric acid is added to aqueous solution of nitrate and/or acetate of metallic elements so as to be dissolved, in which citric acid merely coexists with the metallic nitrate and/or metallic acetate in the aqueous solution. Accordingly, no citrate has been produced in the aqueous solution. Citrate is produced for the first time when the aqueous solution is heated to be concentrated and dehydrated. During this heating process, a large amount of harmful gases such as nitric acid (HNO.sub.3) gas, nitrogen oxides (NOx) gas, and acetic acid (CH.sub.3 COOH) gas are evolved. Furthermore, after the dehydration, the citrate is gelled and strongly adhered to a container. Thus the citrate is sticky and difficult to be treated. Additionally, during calcination, the citrate becomes into an oil state and will vigorously burn with black smoke, which is very dangerous. The thus calcined citrate is in a ceramel state and therefore tends to swell so as to be very difficult to be treated. Moreover, although the above-discussed methods can be carried out in an experimental scale, they are difficult to be carried out in an industrial scale because of raising many problems from view points of environmental pollution and producing devices.